Allow the plaster ceiling to dry for at least 30 days before attempting to paint the surface to prevent the mixing of the paint and plaster. After 30 days, prime the ceiling surface just as you would any drywall surface before painting. Use a primer that goes with the type of paint that you plan to use on the plaster ceiling, such as latex- or oil-based, to prime. Apply a single coat of primer, allow the primer to dry and sand over the primer to roughen it. You then will want to apply one to two more layers of primer, letting the primer dry and sanding between each layer.
When buying paint for a plaster ceiling, select a paint that is specifically labeled for ceilings. Ceiling paint is thicker, which prevents the paint from dripping as you try to apply it. Cover the floor of the room with painter's tarps in case of drips, and line the walls or molding that touches the ceiling with masking tape to prevent paint from getting on the surface. Begin the paint job at the edges of the room, using a paintbrush to paint 4 or 5 inches out from the wall all around the room, and use a paint roller with an extension handle to paint the remainder of the ceiling.
Apply at least two coats of paint to a plaster ceiling for complete coverage, and allow the first coat to dry before adding the second. If the paint is not the color that you would like after the second coat, continue to add paint coats until the ceiling is the color you desire. Though most ceiling paints do not require any type of finishing layer for the paint job to hold up, if you are painting a plaster ceiling in a kitchen or bathroom where humidity will be present, a waterproof sealant can be beneficial.
If you have a talent for painting, you can paint a new plaster ceiling during the installation process. This painting technique, known as fresco, is accomplished by applying paint to wet plaster, which allows the coloring to dry right into the plasterwork, creating a paint that holds up for as long as the plasterwork holds. The fresco technique of painting plaster is generally used in the design of murals and other ceiling artwork.